1. Field of the Invention
This invention relates to weld stud fasteners. More specifically, this invention relates to stand-off weld studs configured to enable attachment of components or assemblies to metal structures, such as the interior of a ship.
2. Description of the Prior Art
Weld studs are typically metallic fasteners that are end-welded to a base attachment structure, such as a metal sheet, plate, or beam, using a weld stud welding process. The weld stud welding process allows weld studs to be welded to various metals to eliminate the need for through holes or possibly a requirement for having access to the opposite side of the base material to which the weld stud is being welded. Once attached, the versatility of the weld studs becomes apparent in a wide variety of fastening applications. For example, weld studs are used in appliance and automotive body manufacturing, where the use of screws or alternative fasteners may be undesirable for aesthetic or structural reasons. Bridge builders use weld studs as concrete anchors to hold expansion joints in place. Perhaps the most voluminous utilization of weld studs occurs in the construction industry. There, the headed weld studs are welded to steel beams of steel and concrete girder systems to both prevent shear slippage of concrete on top of the beams and add strength to the systems.
Another highly desirable feature of weld studs is that they may be implemented without puncturing a hole in the attendant base attachment structure. Thus, weld stud welding arguably revolutionized the shipbuilding industry, where the weld studs are ubiquitous. In shipbuilding applications, the weld studs are used to hold or support a variety of loads. For example, shipbuilders use the weld studs to attach components and assemblies, such as cable hangers, pipes, and electrical installations to interior walls, bulkheads, or overhead decks of a vessel.
The weld studs are typically welded to a base attachment structure, and an assembly or load is attached to the head (unwelded free end) of the weld stud. For weld studs having external threads, the attachment is typically made using a nut. For weld stud welds having internal threads, a threaded bolt is typically installed in a tapped hole of the weld stud. The attachment is made using a nut on weld studs having external threads, or using a threaded bolt into weld studs having internal threads.
An extensive range of prior art weld stud designs having both external and internal threads for weld stud welding to ship and other military equipment is covered in detail by Military Specification MIL-S-24149 of the United States Armed Forces. Internally threaded weld studs with reduced diameter weld bases are Class 5 weld studs. Internally threaded weld studs that have a single diameter, and hence lack the reduced diameter weld base, are Class 5A weld studs.
Traditional internally threaded weld studs for either commercial or military use are configured to receive the threaded bolt such that the threaded portion of the bolt and the complementary threaded portion of the weld stud are in direct contact throughout the length of the bolt position installed in the weld stud. Such an assembly is often robust and desirable under static conditions, but it may also be limited in its capacity to sustain extreme dynamic forces such as those effectuated by an exploded ordinance.
In the case of military shipbuilding applications, weld studs (among other equipment mounted on ships) must demonstrate a capacity to withstand mechanical shock loads that could be sustained during wartime service. The United States Armed Forces, for example, uses Military Specification MIL-S-901D to account for such requirements in the testing of equipment mounted on its ships. Mechanical shock introduces physical stresses that may cause the equipment to fail in shear or tension, depending in part on the material comprising the equipment. Therefore, it is important that such equipment, including fasteners, resist the deleterious effects of these shock forces in operation.
Accordingly, there is an unmet need in the art for an improved internally threaded weld stud suitable for efficient installation in military shipbuilding applications, wherein the weld stud provides both a robust load bearing capacity under static conditions while concurrently maintaining its structural integrity by providing the ductility and flexibility necessary to withstand substantial mechanical shock forces acting on the weld stud. Moreover, there is an unmet need for an internally threaded weld stud that is able to cushion and absorb shock loads, rather than transmitting loads, that are greater than the capacity and strength of the bolts installed in the weld stud designs of the prior art.